Polymers of alpha-olefins prepared in the presence of heterogeneous catalyst systems, as for example, polypropylene prepared using a catalyst comprised of diethylaluminum chloride and titanium trichloride, contain greater or lesser amounts of low-molecular-weight and, particularly, amorphous components which, when taken alone, are viscous oils or soft, tacky solids. The presence of these alkane-soluble materials in the polymers leads to difficulties during their fabrication and to inferior physical properties of the finished item, and hence are almost always removed in commercial processes for the production of polypropylene.
In the past a number of cyclic, sterically hindered amines have been reported in the patent literature as useful (c) components, supra, to reduce the alkane-soluble fraction produced in the polymerization of alpha-olefins. See e.g., Boor, U.S. Pat. No. 3,240,773 and Hoeg et al., British Pat. No. 867,139. Additionally, Watt, U.S. Pat. No. 3,449,263 has taught the addition of bis-(trialkyltin) sulfides to mono-(hydrocarbyl)-aluminum dihalide-titanium trihalide mixtures for the polymerization of ethylene or an alpha-olefin to convert such polymerization ineffective mixtures into polymerization catalysts. However, Watt's Examples, particularly when read together with Avisun, British Pat. No. 966,678, show the alkyltin sulfide employed, bis-tributyltin sulfide, is ineffective for the use claimed.
In the above-referred to literature no claim has been made that use of such amine or organotin compound will reduce the alkane-soluble polymers produced to a point where no extraction would be necessary in the commercial process while still maintaining a commercially feasible yield of crystalline polymer. A polyolefin product containing about two percent or less of n-hexane-soluble polymer would not require a separation step prior to commercial use and hence would be economically advantageous.
Now it has been found that by using a (c) component comprising a sterically-hindered, cyclic amine and an organotin sulfide, a highly crustalline, substantially hexane-insoluble, poly alpha-olefin can be made in yields which are equal to those presently obtained in the better slurry-type processes. In addition, this catalyst functions well in polymerization processes wherein the olefin is polymerized directly from the vapor or liquid phase.